package com.iiapk.gridview.view;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.Scroller;

public class ScrollLayout extends ViewGroup {
	
	private static final String TAG = "ScrollLayout";
	private static final int TOUCH_STATE_REST = 0;
    private static final int TOUCH_STATE_SCROLLING = 1;
    private static final int SNAP_VELOCITY = 600;
    
    public static int curentPage;
	public static int countPages;

    private float mLastMotionX;
    private float mLastMotionY;
    private int mTouchState = TOUCH_STATE_REST;
    private int mCurScreen;
    private int mDefaultScreen;
	//记录touch事件中被认为是滑动事件前的最大可滑动距离
    private int mTouchSlop;
    
    private Scroller mScroller;
	private OnScrollToScreenListener scrollToScreenListener;
	private VelocityTracker mVelocityTracker;
	private PageListener pageListener;

	public ScrollLayout(Context context, AttributeSet attrs) {
		super(context, attrs);
		mScroller = new Scroller(context);
		mCurScreen = mDefaultScreen;
		mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
	}
	
	/**
	 * 方法名称：snapToDestination 
	 * 方法描述：根据当前位置滑动到相应界面
	 */
	public void snapToDestination() {
		final int screenWidth = getWidth();
		final int destScreen = (getScrollX() + screenWidth / 2) / screenWidth;
		snapToScreen(destScreen);
	}
	
	 /**
     * 方法名称：snapToScreen 
     * 方法描述：滑动到到第whichScreen（从0开始）个界面，有过渡效果
     */
	public void snapToScreen(int whichScreen) {
		// get the valid layout page
		whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
		if (getScrollX() != (whichScreen * getWidth())) {
			final int delta = whichScreen * getWidth() - getScrollX();
			mScroller.startScroll(getScrollX(), 0, delta, 0,Math.abs(delta) * 2);
			mCurScreen = whichScreen;
			if(mCurScreen>curentPage){
				curentPage = whichScreen;
				pageListener.page(curentPage);
			}else if(mCurScreen<curentPage){
				curentPage = whichScreen;
				pageListener.page(curentPage);
			}
			pageListener.page(whichScreen);
			// Redraw the layout
			invalidate();
		}
	}
	
	 /**
     * 方法名称：setToScreen 
     * 方法描述：指定并跳转到第whichScreen（从0开始）个界面 
     */
   public void setToScreen(int whichScreen) {
	   	whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
	   	mCurScreen = whichScreen;
	   	//scrollTo(whichScreen * getWidth(), 0);
	   	scrollTo(240, 0);
	   	doScrollAction(whichScreen);        
    }
   
   @Override
   public void computeScroll(){
       if (mScroller.computeScrollOffset()) {
    	   scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
    	   postInvalidate();
       }          
   }
   
   /** 
    * 方法名称：doScrollAction 方法描述：当滑动切换界面时执行相应操作
    * @param index
    */
   private void doScrollAction(int whichScreen) {
	   if (scrollToScreenListener != null) {
		   scrollToScreenListener.doAction(whichScreen);
	   }         
   }	

    public int getCurScreen() {
    	return mCurScreen;
    }
    
    public void setCurScreen(int position) {
        mCurScreen = position;
    }
    
    public void setOnScrollToScreenListener(OnScrollToScreenListener scrollToScreenListener) {
    	this.scrollToScreenListener = scrollToScreenListener;
    }
    
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
    	Log.e(TAG, "onInterceptTouchEvent-slop:" + mTouchSlop);
    	 final int action = ev.getAction();
    	 //Scrolling...let event stay here 
         if (action == MotionEvent.ACTION_MOVE && mTouchState != TOUCH_STATE_REST) {
                  return true;
         }
         final float x = ev.getX();
         final float y = ev.getY();
         switch (action) {
	         case MotionEvent.ACTION_DOWN:
	             mLastMotionX = x;
	             mLastMotionY = y;
	             //init mTouchState
	             mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING; 
	             break;
	         case MotionEvent.ACTION_MOVE:
	             final int xDiff = (int) Math.abs(mLastMotionX - x);
	             if (xDiff > mTouchSlop) { 
	            	 if (Math.abs(mLastMotionY - y) / Math.abs(mLastMotionX - x) < 1)
	            		 mTouchState = TOUCH_STATE_SCROLLING;
	            }
	            break;
		    case MotionEvent.ACTION_CANCEL:
		    case MotionEvent.ACTION_UP:
	             mTouchState = TOUCH_STATE_REST;
	             break;
         }
         return mTouchState != TOUCH_STATE_REST;
    }
    
    @Override
	public boolean onTouchEvent(MotionEvent event) {
    	if (mVelocityTracker == null) {
			mVelocityTracker = VelocityTracker.obtain();
		}
		mVelocityTracker.addMovement(event);
		final int action = event.getAction();
		final float x = event.getX();
		
		switch (action) {
			case MotionEvent.ACTION_DOWN:
				if (!mScroller.isFinished()) {
					mScroller.abortAnimation();
				}
				mLastMotionX = x;
				break;
			case MotionEvent.ACTION_MOVE:
				int deltaX = (int) (mLastMotionX - x);
				mLastMotionX = x;
				scrollBy(deltaX, 0);
				break;
			case MotionEvent.ACTION_UP:
				final VelocityTracker velocityTracker = mVelocityTracker;
				velocityTracker.computeCurrentVelocity(1000);
				int velocityX = (int) velocityTracker.getXVelocity();

				if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {
					// Fling enough to move left
					snapToScreen(mCurScreen - 1);
				} else if (velocityX < -SNAP_VELOCITY && mCurScreen < getChildCount() - 1) {
					// Fling enough to move right
					snapToScreen(mCurScreen + 1);
				} else {
					snapToDestination();
				}
				if (mVelocityTracker != null) {
					mVelocityTracker.recycle();
					mVelocityTracker = null;
				}
				mTouchState = TOUCH_STATE_REST;
				break;
			case MotionEvent.ACTION_CANCEL:
				mTouchState = TOUCH_STATE_REST;
				break;
		}
		return true;
    }

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		/*
		 * int measuredWidth = measureWidth(widthMeasureSpec); 
		 * int measuredHeight = measureHeight(heightMeasureSpec);
		 * setMeasuredDimension(measuredHeight, measuredWidth);
		 */
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
		final int width = MeasureSpec.getSize(widthMeasureSpec);
		final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
		if (widthMode != MeasureSpec.EXACTLY) {
			throw new IllegalStateException(
					"ScrollLayout only canmCurScreen run at EXACTLY mode!");
		}

		final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
		if (heightMode != MeasureSpec.EXACTLY) {
			throw new IllegalStateException(
					"ScrollLayout only can run at EXACTLY mode!");
		}

		final int count = getChildCount();
		for (int i = 0; i < count; i++) {
			getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
		}
		scrollTo(mCurScreen * width, 0);
	}
	
	/*private int measureWidth(int measureSpec) {
		int specMode = MeasureSpec.getMode(measureSpec);
		int specSize = MeasureSpec.getSize(measureSpec);
		int result = 0;
		if (specMode == MeasureSpec.AT_MOST) {
			// use all the available space
			result = specSize;
		} else if (specMode == MeasureSpec.EXACTLY) {
			// If your control can fit within these bounds return that value.
			result = specSize;
		}
		return result;
	}*/

	/*private int measureHeight(int measureSpec) {
		int specMode = MeasureSpec.getMode(measureSpec);
		int specSize = MeasureSpec.getSize(measureSpec);
		int result = 0;
		if (specMode == MeasureSpec.AT_MOST) {
			result = specSize;
		} else if (specMode == MeasureSpec.EXACTLY) {
			result = specSize;
		}
		return result;
	}*/

	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b) {
		int childLeft = 0;
		final int childCount = getChildCount();
		for (int i = 0; i < childCount; i++) {
			final View childView = getChildAt(i);
			if (childView.getVisibility() != View.GONE) {
				final int childWidth = childView.getMeasuredWidth();
				// childView.layout(l, t, r, b);
				childView.layout(childLeft, 0, childLeft + childWidth,childView.getMeasuredHeight());
				childLeft += childWidth;
			}
		}
	}
	
	/** 
	* 接口名称：OnScrollToScreen 
	* 接口描述：当滑动到某个界面时可以调用该接口下的doAction()方法执行某些操作 
	*/
	public abstract interface OnScrollToScreenListener {
        public void doAction(int whichScreen);
	}
	
	public void setPageListener(PageListener pageListener) {
		this.pageListener = pageListener;
	}
	
	public interface PageListener {
		void page(int page);
	}

}
